docs: def _keplerian_mean_to_keplerian(cls, coord, center):
          """Conversion from Mean Keplerian to True Keplerian
          """
          a, e, i, Ω, ω, M = coord
          E = cls._m_to_e(e, M)
          cos_ν = (cos(E) - e) / (1 - e * cos(E))
          sin_ν = (sin(E) * sqrt(1 - e**2)) / (1 - e * cos(E))
  
          ν = arctan2(sin_ν, cos_ν) % (np.pi * 2)
  
          return np.array([a, e, i, Ω, ω, ν], dtype=float)